1. Field of the Invention
The present invention relates to an X-ray and electron beam source using an electron accelerator, and more particularly to the source having a continuous wave electron accelerator which can accelerate electrons to 10 MeV with power levels up to several hundreds kW and a beam irradiator which can irradiate the electron beam toward a target in a radial direction thereof.
2. Description of the Related Art
Industrial electron beam accelerator can be classified into a DC(direct current) accelerating type and a RF(radio-frequency) accelerating type in accordance to the accelerating method.
The former accelerates electrons by applying a DC voltage corresponding to the desired beam energy between electrodes, and it can obtain a continuous wave beam and has high efficiency of energy conversion. However, the size of apparatus must be enlarged according to the desired high energy, thus it can be used only for below 5 MeV beam energy.
The latter accelerates electrons by using travelling waves or standing waves, and can obtain high energy beam with a relatively small apparatus in comparison to the former type.
By the way, for industrial use the beam energy of the accelerator is preferably lower than 10 MeV, owing to the activation of the irradiated object. Thus the RF accelerating type for industrial use is mainly used for between 5 and 10 MeV.
Industrial accelerators for 10 MeV in use includes RF Linac(radio frequency linear accelerator) and "Rhodotron" which was proposed in document WO-A-88/09597(Atomic Energy Commission).
The RF Linac uses the accelerating principle of high energy linear electron accelerator which is widely used in science study, and accelerates electrons using travelling waves.
In RF Linac with a high power, beam may not be stable, since the accelerating cavity is distorted owing to non-uniform heat resulting from beam loss and RF power dissipation in the cavity wall. Because of this problem, the average output power of RF Linac is limited up to about 25 kW.
Whereas, since Rhodotron has a coaxial cavity using electromagnetic waves with low frequency having wavelength of several meters, heat load of cavity resulting from the RF power loss is smaller than that of RF Linac, which means that it can obtain high power electron beam. Therefore Rhodotron is mainly used for the industrial field requiring 10 MeV energy and more than 25 kW beam power.
However, since the standing wave mode for accelerating electrons in Rhodotron is TEM(transverse electromagnetic wave) mode, which may result intersection of plurality of beams around the center of the accelerating cavity, the beam loss may happen in case of high output power.
The beam irradiator is an apparatus for irradiating beams accelerated by accelerators to irradiate medical devices, cables, food, and so on. When it is used as an electron beam irradiator, it has an extracting window in the beam extracting part to maintain pressure difference between the atmospheric pressure and vacuum inside the beam irradiator, and when it is used as an X-ray irradiator, it has a target for producing X-rays. Therefore, except extracting part, the structures of the irradiators for X-ray source and electron beam source are same with each other.
A conventional X-ray irradiator irradiates electron beams 74 to impact a flat plate shaped X-ray target 76, through which the electron beams are converted into X-rays and are irradiated to the objects, as shown in FIG. 5.
By the way, according to above prior technique, X-rays are irradiated to the object only in one direction, which means that irradiation of X-rays is not uniform, which damages the object and deforms the object owing to local heating.
In order to solve the above problems, a supplementary apparatus for rotating the object while irradiating it may be prepared. But, it is inconvenient and the kinds of applicable objects for the apparatus are limited.
Furthermore, in case of producing X-rays by Bremsstrahlung accelerated electrons with energy above several MeV produce X-rays that have maximum intensity in the forward direction with narrow angle.
However, according to the prior art, since the scanning magnets deflect electrons during accelerating, before impacting the flat target 76, the incident electrons can not impact the target 76 perpendicularly. Thus the produced X-rays are not irradiated with maximum intensity, which results in loss of X-rays.